The Network.Socket module is for when you want full control over
sockets. Essentially the entire C socket API is exposed through
this module; in general the operations follow the behaviour of the C
functions of the same name (consult your favourite Unix networking book).

A higher level interface to networking operations is provided
through the module Network.

Resolve a host or service name to one or more addresses.
The AddrInfo values that this function returns contain SockAddr
values that you can pass directly to connect or
bindSocket.

This function is protocol independent. It can return both IPv4 and
IPv6 address information.

The AddrInfo argument specifies the preferred query behaviour,
socket options, or protocol. You can override these conveniently
using Haskell's record update syntax on defaultHints, for example
as follows:

myHints = defaultHints { addrFlags = [AI_ADDRCONFIG, AI_CANONNAME] }

Values for addrFlags control query behaviour. The supported
flags are as follows:

The HostName argument must be a numeric
address in string form, and network name lookups will not be
attempted.

Note: Although the following flags are required by RFC 3493, they
may not have an effect on all platforms, because the underlying
network stack may not support them. To see whether a flag from the
list below will have any effect, call addrInfoFlagImplemented.

AI_NUMERICSERV

The ServiceName argument must be a port
number in string form, and service name lookups will not be
attempted.

AI_ADDRCONFIG

The list of returned AddrInfo values will
only contain IPv4 addresses if the local system has at least
one IPv4 interface configured, and likewise for IPv6.

AI_V4MAPPED

If an IPv6 lookup is performed, and no IPv6
addresses are found, IPv6-mapped IPv4 addresses will be
returned.

AI_ALL

If AI_ALL is specified, return all matching IPv6 and
IPv4 addresses. Otherwise, this flag has no effect.

You must provide a Just value for at least one of the HostName
or ServiceName arguments. HostName can be either a numeric
network address (dotted quad for IPv4, colon-separated hex for
IPv6) or a hostname. In the latter case, its addresses will be
looked up unless AI_NUMERICHOST is specified as a hint. If you
do not provide a HostName value and do not set AI_PASSIVE as
a hint, network addresses in the result will contain the address of
the loopback interface.

If the query fails, this function throws an IO exception instead of
returning an empty list. Otherwise, it returns a non-empty list
of AddrInfo values.

There are several reasons why a query might result in several
values. For example, the queried-for host could be multihomed, or
the service might be available via several protocols.

Note: the order of arguments is slightly different to that defined
for getaddrinfo in RFC 2553. The AddrInfo parameter comes first
to make partial application easier.

Resolve an address to a host or service name.
This function is protocol independent.

The list of NameInfoFlag values controls query behaviour. The
supported flags are as follows:

NI_NOFQDN

If a host is local, return only the
hostname part of the FQDN.

NI_NUMERICHOST

The name of the host is not
looked up. Instead, a numeric representation of the host's
address is returned. For an IPv4 address, this will be a
dotted-quad string. For IPv6, it will be colon-separated
hexadecimal.

NI_NUMERICSERV

The name of the service is not
looked up. Instead, a numeric representation of the
service is returned.

NI_NAMEREQD

If the hostname cannot be looked up, an IO error
is thrown.

NI_DGRAM

Resolve a datagram-based service name. This is
required only for the few protocols that have different port
numbers for their datagram-based versions than for their
stream-based versions.

Hostname and service name lookups can be expensive. You can
specify which lookups to perform via the two Bool arguments. If
one of these is False, the corresponding value in the returned
tuple will be Nothing, and no lookup will be performed.

If a host or service's name cannot be looked up, then the numeric
form of the address or service will be returned.